<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Title</title>
  <script>
    console.log('-----------------')
    if (true) {
      console.log('true');
    }
    if (0) {//false
      console.log('0');
    }
    if (!0) {//true
      console.log('!0');
    }
    if ('') {//false
      console.log('空字符串');
    }
    if ('abc') {//true
      console.log('abc');
    }
  </script>
</head>
<body>

</body>
</html>